Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read symbol targets, such as one- and/or two-dimensional bar code symbols, each bearing elements, e.g., bars and spaces, of different widths and reflectivities, to be decoded, as well as other targets, such as forms, documents, labels, receipts, signatures, drivers' licenses, identification badges, payment/loyalty cards, and the like, each bearing one or more form fields, typically containing alphanumeric characters, images, or bar code symbols.
A known exemplary imaging reader includes a housing, either held by a user in the handheld mode, or supported on a support, such as a stand, a cradle, a docking station, or a support surface, in the hands-free mode; a window supported by the housing and aimed at the target; and an imaging engine or module supported by the housing and having a solid-state imager (or image sensor or camera) with a sensor array of photocells or light sensors (also known as pixels), and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged along an imaging axis through the window over a field of view, and for projecting the return light onto the sensor array to initiate capture of an image of the target over a range of working distances in which the target can be read. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of pixel data over the field of view. These electrical signals are decoded and/or processed by a programmed microprocessor or controller into information related to the target being read, e.g., decoded data indicative of a symbol, or characters or marks indicative of text in a form field of a form, or into a picture indicative of a picture on the form. A trigger is typically manually activated by the user to initiate reading in the handheld mode of operation. Sometimes, an object sensing assembly is employed to automatically initiate reading whenever a target enters the field of view in the hands-free mode of operation. At other times, the image sensor itself may be employed to detect entry of the target into the field of view.
In the hands-free mode, the user may slide or swipe the target past the window in either horizontal and/or vertical and/or diagonal directions in a “swipe” mode. Alternatively, the user may present the target to an approximate central region of the window in a “presentation” mode. The choice depends on the type of target, operator preference, or on the layout of a workstation in which the reader is used. In the handheld mode, the user holds the reader in his or her hand at a certain working distance from the target to be imaged and initially aims the reader at the target. The user may first lift the reader from a countertop or like support surface, or from a support, such as a stand, a cradle, or a docking station. Once reading is completed, the user may return the reader to the countertop, or to the support, to resume hands-free operation.
Although the known imaging readers are generally satisfactory for their intended purpose, one concern relates to different reading performance requirements for the handheld and hands-free modes of operation. It is known to configure an imaging reader with a two-dimensional image sensor having a full or high resolution of, for example, 1280 pixels×960 pixels. Cost-effective image sensor interfaces, e.g., a single channel mobile industry processor interface (MIPI) serial bus, or a single channel parallel bus, limit the frame rate of this high resolution image sensor to a low frame rate of about 30 frames per second, or less. Thus, the data clock frame rate to get pixel information off of the image sensor is limited. At a fixed frame rate, more pixels means more time to read a full frame and, concomitantly, less frames are available in a given time period.
Such a full resolution is desirable for the handheld mode, because it avoids truncating the range of working distances in which targets can be read. In the absence of focus limitations, the working range of an imaging reader is dependent on the reader's ability to distinguish among individual elements of the target. For a given field of view of the image sensor, more pixels allow smaller target elements to be resolved. This not only means smaller in terms of physical dimension of the target elements, but also smaller in terms of the apparent size of a target further away from the reader. Thus, a higher pixel count of an image sensor for a given field of view provides a longer working distance range. However, in the hands-free mode, an extended, long range of working distances, e.g., over one foot, is not desired and, indeed, a very limited, short range, e.g., on the order of a few inches or less, is preferred, because the targets to be read are typically brought to the immediate vicinity of the reader. An imaging reader configured for an optimum long working distance range for handheld operation is, therefore, at a disadvantage when operated in the hands-free mode.
Similarly, such a low frame rate is not desirable in the hands-free mode, especially when the image sensor itself is employed to detect motion and entry of the target into the field of view. A faster frame rate would be desirable in the hands-free mode for more aggressive target detection. An imaging reader configured for a low frame rate for handheld operation is, therefore, at a disadvantage when operated in the hands-free mode.
Accordingly, there is a need for an apparatus for, and a method of, optimizing target reading performance parameters, such as imager resolution, frame rate, and working distance range, during operation in both the handheld and hands-free modes, and for changing such reading performance parameters to different values in each mode to optimize the reading performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.